Split Allow_missing_dependencies from Unbundled_build

There are stripped down branches used to build other things than just
unbundled apps (like the AOSP llvm branch used to build llvm prebuilts).

Change-Id: Id772eac8c4622458591b52f9f27723fdb83f9a85
diff --git a/common/config.go b/common/config.go
index ef59cf7..0812903 100644
--- a/common/config.go
+++ b/common/config.go
@@ -301,7 +301,7 @@
 }
 
 func (c *config) AllowMissingDependencies() bool {
-	return Bool(c.ProductVariables.Unbundled_build)
+	return Bool(c.ProductVariables.Allow_missing_dependencies)
 }
 
 func (c *config) SkipDeviceInstall() bool {